Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. We’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm coax. The resulting 50-Ω differential mode goes into a machined tapered structure that maintains 50 ohms while spreading out the mode to match the 25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with
a dielectric constant of 3.5ish. This means that it’s hard to iterate—we get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out
to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge,
so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. >hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 >gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. >We’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm >coax. The resulting 50-? differential mode goes into a machined tapered >structure that maintains 50 ohms while spreading out the mode to match the >25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with
a dielectric constant of 3.5ish. This means that it’s hard to iterate—we
get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out
to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge,
so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and >there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
On 1/22/2025 10:43 PM, Phil Hobbs wrote:
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g.
hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000
gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. >> We’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm
coax. The resulting 50-Ω differential mode goes into a machined tapered
structure that maintains 50 ohms while spreading out the mode to match the >> 25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with >> a dielectric constant of 3.5ish. This means that it’s hard to iterate—we >> get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out
to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge, >> so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and
there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
Cold you please test ninja turtle ooze and report back. It's some kind
of guar gum/vinyl acetate and borate gelatin:
<https://en.wikipedia.org/wiki/Flubber_(material)>
<https://www.amazon.com/Teenage-Mutant-Ninja-Turtles-83700CO/dp/B0C6RFTJF2/>
bitrex <user@example.net> wrote:
On 1/22/2025 10:43 PM, Phil Hobbs wrote:
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. >>> hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 >>> gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. >>> We’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm
coax. The resulting 50-Ω differential mode goes into a machined tapered >>> structure that maintains 50 ohms while spreading out the mode to match the >>> 25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with >>> a dielectric constant of 3.5ish. This means that it’s hard to iterate—we
get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out >>> to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge, >>> so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and >>> there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
Cold you please test ninja turtle ooze and report back. It's some kind
of guar gum/vinyl acetate and borate gelatin:
<https://en.wikipedia.org/wiki/Flubber_(material)>
<https://www.amazon.com/Teenage-Mutant-Ninja-Turtles-83700CO/dp/B0C6RFTJF2/> >>
Nah, Western religious art, particularly Italian Renaissance stuff, leaves
me cold. Cute little cupids representing the glorious cherubim, Madonnas modeled after artists’ paramours, corrupt prelates and donors painted into biblical scenes, blech.
Cheers
Phil Hobbs
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 gees, and over its lifetime it might see around 1E6 blows. Challenging.
On Thu, 23 Jan 2025 03:43:03 -0000 (UTC), Phil Hobbs wrote:
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g.
hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000
gees, and over its lifetime it might see around 1E6 blows. Challenging.
Have you considered using a mechanical low pass filter on your slide
hammer, a pad on either the hammer or anvil striking surfaces? Rawhide
faced iron hammers are very good at driving stakes into very hard soil without the severe impulse of a metal on metal impact, and while rawhide might not be good for 1E6 cycles you could try rubber sheet or heavy
gasket material, tune the response by changing thickness and hardness to suit. Presumably the same slide hammer is used for removal, so you would want to pad the upper surface also.
Between padding the hammer and compliant mounting of your circuit (two
series low pass filters) you should be able to keep the acceleration of
your circuit module to something reasonable.
Hard epoxy potting compounds can put a lot of stress on parts from differential thermal expansion, sometimes a compliant layer of a more flexible material is used over sensitive components before potting with
hard epoxy.
Glen
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. We?re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm coax. The resulting 50-? differential mode goes into a machined tapered structure that maintains 50 ohms while spreading out the mode to match the 25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with
a dielectric constant of 3.5ish. This means that it?s hard to iterate?we
get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out
to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge,
so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
Glen Walpert <nospam@null.void> wrote:
On Thu, 23 Jan 2025 03:43:03 -0000 (UTC), Phil Hobbs wrote:Thanks, that’s interesting.
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. >>> hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 >>> gees, and over its lifetime it might see around 1E6 blows. Challenging.
Have you considered using a mechanical low pass filter on your slide
hammer, a pad on either the hammer or anvil striking surfaces? Rawhide
faced iron hammers are very good at driving stakes into very hard soil
without the severe impulse of a metal on metal impact, and while rawhide
might not be good for 1E6 cycles you could try rubber sheet or heavy
gasket material, tune the response by changing thickness and hardness to
suit. Presumably the same slide hammer is used for removal, so you would
want to pad the upper surface also.
Between padding the hammer and compliant mounting of your circuit (two
series low pass filters) you should be able to keep the acceleration of
your circuit module to something reasonable.
Hard epoxy potting compounds can put a lot of stress on parts from
differential thermal expansion, sometimes a compliant layer of a more
flexible material is used over sensitive components before potting with
hard epoxy.
Glen
We’ve thought about a pad, but haven’t done any studies yet. The problem of
hard epoxy ripping things apart is pretty well known, I think—as you say, the fix is a thin layer of RTV or something like that.
I didn’t know about rawhide-faced hammers, which sound cool. With hard materials, the pulse width equals the length of the impactor divided by the speed of sound in the material, which in this case is just about 20us. The force is the change of momentum divided by the pulse width.
If the pad compresses by 1 mm when the slide hammer arrives at 2 m/s, the pulse width is about 500us, so the peak acceleration would be more like
1000 gees.
Cheers
Phil Hobbs
On 1/25/25 8:22 AM, Phil Hobbs wrote:
Glen Walpert <nospam@null.void> wrote:
On Thu, 23 Jan 2025 03:43:03 -0000 (UTC), Phil Hobbs wrote:Thanks, that’s interesting.
Simon and I are working on a TDR based soil moisture sensor forHave you considered using a mechanical low pass filter on your slide
agriculture. Like many such things, it uses two parallel tines made of >>>> 18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. >>>> hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 >>>> gees, and over its lifetime it might see around 1E6 blows. Challenging. >>>
hammer, a pad on either the hammer or anvil striking surfaces? Rawhide
faced iron hammers are very good at driving stakes into very hard soil
without the severe impulse of a metal on metal impact, and while rawhide >>> might not be good for 1E6 cycles you could try rubber sheet or heavy
gasket material, tune the response by changing thickness and hardness to >>> suit. Presumably the same slide hammer is used for removal, so you would >>> want to pad the upper surface also.
Between padding the hammer and compliant mounting of your circuit (two
series low pass filters) you should be able to keep the acceleration of
your circuit module to something reasonable.
Hard epoxy potting compounds can put a lot of stress on parts from
differential thermal expansion, sometimes a compliant layer of a more
flexible material is used over sensitive components before potting with
hard epoxy.
Glen
We’ve thought about a pad, but haven’t done any studies yet. The problem of
hard epoxy ripping things apart is pretty well known, I think—as you say, >> the fix is a thin layer of RTV or something like that.
I didn’t know about rawhide-faced hammers, which sound cool. With hard
materials, the pulse width equals the length of the impactor divided by the >> speed of sound in the material, which in this case is just about 20us. The >> force is the change of momentum divided by the pulse width.
If the pad compresses by 1 mm when the slide hammer arrives at 2 m/s, the
pulse width is about 500us, so the peak acceleration would be more like
1000 gees.
Cheers
Phil Hobbs
There are also "Dead-Blow Hammers" used for automotive bodywork. They
spread the strike over a longer period, often by being hollow and filled
with steel shot.
https://en.wikipedia.org/wiki/Dead-blow_hammer
kw
On Thu Jan 23 03:43:03 2025 Phil Hobbs wrote:
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g.
hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000
gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. >> We?re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm >> coax. The resulting 50-? differential mode goes into a machined tapered
structure that maintains 50 ohms while spreading out the mode to match the >> 25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with >> a dielectric constant of 3.5ish. This means that it?s hard to iterate?we
get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out
to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge, >> so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and
there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / >> Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
Just for future reference if you want a material much more rigid than
butter at room temperature you could try cocoa butter. If you make chocolates it is probably already in your pantry :-). It's a mix of triglycerides that melt between about 90 and 100 F so melting it to cast
in place or paint it on or clean it back off would be pretty easy. I
found one online reference using Brave search that listed dielectric constants for some fatty acids and trglycerides similar to those in cocoa butter. They were between about 3 and 3.4 so right in the range you were lookng for. Anyway, I was curious and bored ...
Regards,
Carl
On 1/23/2025 8:41 AM, Phil Hobbs wrote:
bitrex <user@example.net> wrote:
On 1/22/2025 10:43 PM, Phil Hobbs wrote:
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of >>>> 18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. >>>> hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 >>>> gees, and over its lifetime it might see around 1E6 blows. Challenging. >>>>
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun.
We’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm
coax. The resulting 50-Ω differential mode goes into a machined tapered >>>> structure that maintains 50 ohms while spreading out the mode to match the >>>> 25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with >>>> a dielectric constant of 3.5ish. This means that it’s hard to iterate—we
get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out >>>> to be nontrivial. My initial thought was to use alumina lapping powder >>>> (9.3) for filler and vaseline (2.0) for the matrix, but it turned into >>>> clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge, >>>> so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and >>>> there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
Cold you please test ninja turtle ooze and report back. It's some kind
of guar gum/vinyl acetate and borate gelatin:
<https://en.wikipedia.org/wiki/Flubber_(material)>
<https://www.amazon.com/Teenage-Mutant-Ninja-Turtles-83700CO/dp/B0C6RFTJF2/>
Nah, Western religious art, particularly Italian Renaissance stuff, leaves >> me cold. Cute little cupids representing the glorious cherubim, Madonnas
modeled after artists’ paramours, corrupt prelates and donors painted into >> biblical scenes, blech.
Cheers
Phil Hobbs
Right well I don't know if pizza's dielectric properties have been
studied thoroughly but there's been a lot of work done on Jell-O, it
seems pretty customizable. There's always room for Jell-O
<https://pubs.acs.org/doi/pdf/10.1021/j150393a011>
On Thu, 23 Jan 2025 03:43:03 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g.
hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000
gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. >> WeÂ’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm >> coax. The resulting 50-? differential mode goes into a machined tapered
structure that maintains 50 ohms while spreading out the mode to match the >> 25-mm tine spacing.
We've got excellent results with micro-coax on pot cores.
https://www.dropbox.com/scl/fi/o2r1m53es9rb3e7nbsnsr/Pot_Core_TXline.JPG?rlkey=t1g3rp0erz72tqchb99fupfu7&raw=1
https://www.dropbox.com/scl/fi/ie7gzmdwuw4gqgy1pxpjl/TX_1.jpg?rlkey=xllwjn2cg0a0t3yjh90om9ap1&raw=1
For survivability, the whole thing is being potted in very hard epoxy with >> a dielectric constant of 3.5ish. This means that it’s hard to iterate—we >> get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out
to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge, >> so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and
there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
Are you doing a reverse convolution to beautify the step waveform? You
can tolerate a really ugly TDR if you can make a FIR filter to pound
it flat.
KevinJ93 <kevin_es@whitedigs.com> wrote:
On 1/25/25 8:22 AM, Phil Hobbs wrote:
Glen Walpert <nospam@null.void> wrote:
On Thu, 23 Jan 2025 03:43:03 -0000 (UTC), Phil Hobbs wrote:Thanks, that’s interesting.
Simon and I are working on a TDR based soil moisture sensor forHave you considered using a mechanical low pass filter on your slide
agriculture. Like many such things, it uses two parallel tines made of >>>>> 18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. >>>>> hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 >>>>> gees, and over its lifetime it might see around 1E6 blows. Challenging. >>>>
hammer, a pad on either the hammer or anvil striking surfaces? Rawhide >>>> faced iron hammers are very good at driving stakes into very hard soil >>>> without the severe impulse of a metal on metal impact, and while rawhide >>>> might not be good for 1E6 cycles you could try rubber sheet or heavy
gasket material, tune the response by changing thickness and hardness to >>>> suit. Presumably the same slide hammer is used for removal, so you would >>>> want to pad the upper surface also.
Between padding the hammer and compliant mounting of your circuit (two >>>> series low pass filters) you should be able to keep the acceleration of >>>> your circuit module to something reasonable.
Hard epoxy potting compounds can put a lot of stress on parts from
differential thermal expansion, sometimes a compliant layer of a more
flexible material is used over sensitive components before potting with >>>> hard epoxy.
Glen
We’ve thought about a pad, but haven’t done any studies yet. The problem of >>> hard epoxy ripping things apart is pretty well known, I think—as you say, >>> the fix is a thin layer of RTV or something like that.
I didn’t know about rawhide-faced hammers, which sound cool.
With hard
materials, the pulse width equals the length of the impactor divided by the >>> speed of sound in the material, which in this case is just about 20us. The >>> force is the change of momentum divided by the pulse width.
If the pad compresses by 1 mm when the slide hammer arrives at 2 m/s, the >>> pulse width is about 500us, so the peak acceleration would be more like
1000 gees.
Cheers
Phil Hobbs
There are also "Dead-Blow Hammers" used for automotive bodywork. They
spread the strike over a longer period, often by being hollow and filled
with steel shot.
< https://en.wikipedia.org/wiki/Dead-blow_hammer>
kw
I had one of those back at IBM. They seem a bit on the wimpy side for >pounding stakes into hardpan, no?
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g. hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000 gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. We’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm coax. The resulting 50-Ω differential mode goes into a machined tapered structure that maintains 50 ohms while spreading out the mode to match the 25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with
a dielectric constant of 3.5ish. This means that it’s hard to iterate—we get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out
to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge,
so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
On 23/01/2025 2:43 pm, Phil Hobbs wrote:
Simon and I are working on a TDR based soil moisture sensor for
agriculture. Like many such things, it uses two parallel tines made of
18/8 stainless, that form a balanced transmission line.
Ours has a slide hammer for pounding it into really difficult soil, e.g.
hardpan. The measured shock from that is around 1.6E5 m/s**2, i.e. 16000
gees, and over its lifetime it might see around 1E6 blows. Challenging.
Doing <200 ps TDR on a balanced line obviously needs a very wideband balun. >> We’re using a plain ferrite design based on Ferroxcube 61 sleeves on 1.25mm
coax. The resulting 50-Ω differential mode goes into a machined tapered
structure that maintains 50 ohms while spreading out the mode to match the >> 25-mm tine spacing.
For survivability, the whole thing is being potted in very hard epoxy with >> a dielectric constant of 3.5ish. This means that it’s hard to iterate—we >> get one try per apparatus.
Sooooo, I tried making a soft material with that epsilon, which turns out
to be nontrivial. My initial thought was to use alumina lapping powder
(9.3) for filler and vaseline (2.0) for the matrix, but it turned into
clumps by the time it got to 3.0.
Casting about for alternatives, I remembered the butter in the lab fridge, >> so I measured that: 3.8, better than good enough.
We were able to verify the design without doing anything irrevocable, and
there was some left over for the bagels.
Fun.
Cheers
Phil Hobbs
Butter seems to be pretty lossy at RF, but I don't know whether that
matters.
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